A model reconstruction of the Antarctic sea ice thickness and volume changes over 1980–2008 using data assimilation

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. a b s t r a c tSea ice variability in the Southern Ocean has a complex spatio-temporal structure. In a global warming context, the Antarctic sea ice cover has slightly expanded over the recent decades. This increase in sea ice extent results, however, from the sum of positive and negative regional trends and is influenced by a wide range of modes of climate variability. An additional view on sea ice thickness and volume changes would improve our understanding. Still, no large-scale multi-decadal well-sampled record of Antarctic sea ice thickness exists to date. To address this issue, we assimilate real sea ice concentration data into the ocean-sea ice model NEMO-LIM2 using an ensemble Kalman filter and demonstrate the positive impacts on the global sea ice cover. This paper reports the 1980-2008 evolution (monthly anomalies, trends plus their uncertainty ranges) of sea ice volume and thickness in different sectors of the Southern Ocean. We find that the global Antarctic sea ice volume has risen at a pace of 355 AE 338 km 3 /decade (5:6 AE 5:3%/decade) during this period, with an increase in the Ross and Weddell Seas (150 AE 124 and 209 AE 362 km 3 /decade, respectively) and a decrease in the Amundsen-Bellingshausen Seas (À45 AE 54 km 3 /decade). Sea ice volume anomalies co-vary well with extent anomalies, and exhibit yearly to decadal fluctuations. The results stress the need to analyze sea ice changes at the regional level first and then at the hemispheric level.

Evaluation of CryoSat-2 derived sea-ice freeboard over fast ice in McMurdo Sound, Antarctica

“…Due to the scarcity of in situ measurements of Antarctic sea-ice thickness, there is great demand for improved temporal and spatial thickness data through satellite altimeter observations (Zwally and others, 2008;Yi and others, 2011;Kurtz and Markus, 2012;Xie and others, 2013). Such observations support the capability to monitor trends and in turn provide data to model forecasts of future Antarctic sea-ice properties (Massonnet and others, 2013;Holland and others, 2014).…”

Comparing sea ice, hydrography and circulation between NEMO3.6 LIM3 and LIM2

“…Many studies attribute the increase of sea-ice extent to changes in the atmospheric dynamics, mainly by the increasing trend of the Southern Annular Mode, which in turn has strengthened westerly winds around the Antarctic continent and deepened the Amundsen Sea Low. Stronger westerlies effectively spread sea ice to north and a deeper Amundsen Sea Low increases the sea-ice production in the Ross Sea (see for example, Lefebvre and Goosse, 2008;Holland and Kwok, 2012;Massonnet et al, 2013;Turner et al, 2015). Another potential, simultaneously affecting mechanism increasing the seaice extent is the freshening of the Southern Ocean surface, which stabilises the surface layer, reduces the oceanic heat from below and therefore the associated ice melt (see for example Hellmer, 2004;Bintanja et al, 2013).…”

Modeled Trends in Antarctic Sea Ice Thickness

“…Probably the most reliable estimate of recent ice volume trends are from the model of Massonnet et al (2013), which formally optimizes the estimate by assimilating ice concentration data using an ensemble Kalman filter. The results show an overall 1980-2008 increase in ice volume of 36 6 34 km 3 yr…”